Systems and methods for efficient pumping of high-pressure fluids for energy storage and recovery

ABSTRACT

In various embodiments, a mechanical assembly and/or storage vessel is fluidly coupled to a circulation apparatus for receiving pressurized heat-transfer fluid from an outlet at a first elevated pressure, boosting a pressure of the heat-transfer fluid to a second pressure larger than the first pressure, and returning heat-transfer fluid to an inlet at a third pressure.

RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Provisional Patent Application No. 61/328,345, filed Apr. 27, 2010, and is a continuation-in-part of U.S. patent application Ser. No. 12/639,703, filed Dec. 16, 2009, which (i) is a continuation-in-part of U.S. patent application Ser. No. 12/421,057, filed Apr. 9, 2009, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61/148,691, filed Jan. 30, 2009, and U.S. Provisional Patent Application No. 61/043,630, filed Apr. 9, 2008; (ii) is a continuation-in-part of U.S. patent application Ser. No. 12/481,235, filed Jun. 9, 2009, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61/059,964, filed Jun. 9, 2008; and (iii) claims the benefit of and priority to U.S. Provisional Patent Application Nos. 61/166,448, filed on Apr. 3, 2009; 61/184,166, filed on Jun. 4, 2009; 61/223,564, filed on Jul. 7, 2009; 61/227,222, filed on Jul. 21, 2009; and 61/251,965, filed on Oct. 15, 2009. The entire disclosure of each of these applications is hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under IIP-0810590 and IIP-0923633 awarded by the NSF. The government has certain rights in the invention.

FIELD OF THE INVENTION

In various embodiments, the present invention relates to pneumatics, power generation, and energy storage, and more particularly, to compressed-gas energy-storage systems and methods using pneumatic cylinders.

BACKGROUND

Storing energy in the form of compressed gas has a long history and components tend to be well tested, reliable, and have long lifetimes. The general principle of compressed-gas or compressed-air energy storage (CAES) is that generated energy (e.g., electric energy) is used to compress gas (e.g., air), thus converting the original energy to pressure potential energy; this potential energy is later recovered in a useful form (e.g., converted back to electricity) via gas expansion coupled to an appropriate mechanism. Advantages of compressed-gas energy storage include low specific-energy costs, long lifetime, low maintenance, reasonable energy density, and good reliability.

If a body of gas is at the same temperature as its environment, and expansion occurs slowly relative to the rate of heat exchange between the gas and its environment, then the gas will remain at approximately constant temperature as it expands. This process is termed “isothermal” expansion. Isothermal expansion of a quantity of gas stored at a given temperature recovers approximately three times more work than would “adiabatic expansion,” that is, expansion where no heat is exchanged between the gas and its environment, because the expansion happens rapidly or in an insulated chamber. Gas may also be compressed isothermally or adiabatically.

An ideally isothermal energy-storage cycle of compression, storage, and expansion would have 100% thermodynamic efficiency. An ideally adiabatic energy-storage cycle would also have 100% thermodynamic efficiency, but there are many practical disadvantages to the adiabatic approach. These include the production of higher temperature and pressure extremes within the system, heat loss during the storage period, and inability to exploit environmental (e.g., cogenerative) heat sources and sinks during compression and expansion, respectively. In an isothermal system, the cost of adding a heat-exchange system is traded against resolving the difficulties of the adiabatic approach. In either case, mechanical energy from expanding gas must usually be converted to electrical energy before use.

An efficient and novel design for storing energy in the form of compressed gas utilizing near isothermal gas compression and expansion has been shown and described in U.S. Pat. No. 7,832,207 (the '207 patent) and U.S. patent application Ser. No. 12/639,703 (the '703 application), the disclosures of which are hereby incorporated herein by reference in their entireties. The '207 patent and '703 application disclose systems and methods for expanding gas isothermally in staged hydraulic/pneumatic cylinders and intensifiers over a large pressure range in order to generate electrical energy when required. Mechanical energy from the expanding gas is used to drive a hydraulic pump/motor subsystem that produces electricity. Systems and methods for hydraulic-pneumatic pressure intensification that may be employed in systems and methods such as those disclosed in the '207 patent and '703 application are shown and described in U.S. patent application Ser. No. 12/879,595 (the '595 application), the disclosure of which is hereby incorporated herein by reference in its entirety.

In the systems disclosed in the '207 patent and '703 application, reciprocal mechanical motion is produced during recovery of energy from storage by expansion of gas in the cylinders. This reciprocal motion may be converted to electricity by a variety of means, for example as disclosed in the '595 application, as well as in U.S. patent application Ser. No. 12/938,853 (the '853 application), the disclosure of which is hereby incorporated herein by reference in its entirety. Additionally, as described in the '703 application, heat-exchange liquid may be sprayed into a cylinder chamber containing gas undergoing expansion or compression. Such a heat-exchange spray may enable isothermal expansion or compression of gas, with resulting efficiency gains.

The ability of such systems to either store energy (i.e., use energy to compress gas into a storage reservoir) or produce energy (i.e., expand gas from a storage reservoir to release energy) will be apparent to any person reasonably familiar with the principles of electrical and pneumatic machines. However, energy storage systems like those described above may utilize pumps to circulate heat-exchange fluid that either do not accept high-pressure input flows or else do not pump high-pressure inputs with high efficiency, thus diminishing the overall efficiency of the entire system. Specifically, some amount of the work required to pressurize heat-exchange fluid from a low ambient pressure is wasted. Thus, it would be desirable to extract already-pressurized heat-exchange fluid from the system itself, circulate it at its elevated pressure, thermally condition it (if necessary), and recycle it back into the system.

SUMMARY

Embodiments of the present invention provide for the energy-efficient pumping of liquid for the production of liquid sprays used to approximate isothermal expansion and compression inside pneumatic cylinders (and/or pneumatic compartments of various other types of cylinders) or inside other mechanical assemblies for expanding or compressing gas, with resulting gain in the efficiency of the overall energy-storage and energy-recovery process. In the prior art, pumps typically either do not accept high-pressure input flows or else do not pump high-pressure inputs with high efficiency, as mentioned above. Various embodiments of the present invention overcome these disadvantages by enabling the energy-efficient pumping of liquid already at high pressure (e.g., greater than approximately 1,000 pounds per square inch gauge [psig], or even greater than approximately 3,000 psig) to a somewhat higher pressure (e.g., approximately 50 psig higher). Useful applications include, but are not limited to, (1) the provision of a liquid spray into a vessel storing pressurized gas, this spray enabling the transfer of heat to or from the gas, (2) the energy-efficient introduction of liquid sprays into chambers containing pressurized gas, these sprays enabling the approximately isothermal expansion or compression of the gas, and (3) booster pumping in a high-pressure pipeline or between high pressure vessels.

Generally, embodiments of the invention utilize a reciprocating, double-acting, positive-displacement pump having a fluid-filled chamber containing a piston or other mechanism that separates the fluid on one side of the piston from the fluid on the other side, preventing fluid migration from one side to the other while allowing the transfer of force/pressure from one side to the other. The systems described herein may be used to significantly increase the efficiency of, e.g., a variety of compressed-gas energy storage systems. In particular, in a compressed-gas energy storage system, gas is stored at high pressure (e.g., approximately 3,000 psig). This gas may be expanded into a chamber containing a piston or other mechanism that separates the gas on one side of the chamber from the other, preventing gas migration from one chamber to the other while allowing the transfer of force/pressure from one chamber to the next. Such an arrangement of chambers and piston (or other mechanism) is termed a “pneumatic cylinder” or “cylinder” for the purposes of this application. The shaft of the cylinder may be coupled hydraulically or mechanically to a mechanical load (e.g., a hydraulic motor/pump or a crankshaft) that is in turn coupled to an electrical load (e.g., rotary or linear electric motor/generator attached to power electronics and/or directly to the grid or other loads), as described in the '595 and '853 applications.

Gas undergoing expansion tends to cool, while gas undergoing compression tends to heat. Several methods for approximating isothermal expansion and compression may be employed as described, for example, in the '703 application. As disclosed in the '703 application, droplets of a liquid (e.g., water) may be sprayed into the side of a double-acting pneumatic cylinder presently undergoing expansion or compression to expedite heat transfer to or from the gas. As these droplets exchange heat with the gas around them, the temperature of the gas-droplet mixture is either raised or lowered. The liquid is evacuated from the cylinder through a suitable mechanism. The heat-exchange spray droplets may be introduced through spray heads and/or spray rods. If the rate of heat exchange is appropriate, an isothermal process may be approximated.

Embodiments of the invention may be used to efficiently drive a heat-exchange liquid into a pneumatic chamber. In one embodiment, an actuator exerts force on a cylinder's piston to raise the pressure of heat-exchange liquid in one of the cylinder's two chambers. A quantity of work W_(L) is required to raise the pressure of a given volume of liquid in the chamber from some starting (inlet) pressure P_(s) to the injection (outlet) pressure P_(i) (e.g., approximately 3,010 psig, sufficient for spraying into a chamber containing gas at approximately 3,000 psig). To perform this work W_(L) on the liquid, the motor or actuator driving the piston must perform input work W_(i)>W_(L), which is communicated to the liquid with some efficiency η where 0≦η≦1. Specifically, W_(L)=W_(i)η. The amount of work wasted is W_(i)(1−η). In the simplest case, where heat-exchange fluid is drawn from an unpressurized source or reservoir, source pressure P_(s)=0 psig, W_(L) and W_(i) are maximized, and the work wasted by the hydraulic pump W_(i)(1−η) is maximum. If η is constant or approximately constant and source pressure P_(s) is increased, W_(L) and W_(i) are decreased and wasted work W_(i)(1−η) is decreased.

The input-to-pump pressure P_(s) of the heat-exchange fluid may be increased by obtaining the liquid as an output of the pneumatic chamber into which the liquid is being sprayed. That is, the heat-exchange liquid may be recycled by extracting it (at some output pressure P_(s)′>0, equal to the present gas pressure in the pneumatic chamber) from the pneumatic chamber into which it has been sprayed, passing it via pipes through a heat exchanger to raise or lower its temperature, raising its pressure from arrival-at-pump pressure P_(s), <P_(s)′ to injection pressure P_(i), and finally re-injecting the liquid into the chamber from where it came. Filters, valves, reservoirs, and other devices may be included in such a loop without changing its basic purpose and fall within the scope of embodiments of the invention described herein. Particularly if frictional losses in the heat exchanger and other devices that implement the recycling loop amount to less than the work saved at the pump, recycling heat-exchange fluid in this way will increase overall system efficiency.

The above-described mechanism for efficient pumping may be utilized with energy storage and recovery systems featuring one or more cylinder assemblies (i.e., assemblies having one or more closed chambers such as pneumatic, hydraulic, pneumatic/hydraulic cylinders) and/or pressure vessels for storage of compressed gas. A “cylinder assembly” may be a simple cylinder or include multiple cylinders, and may or may not have additional associated components (such as mechanical linkages among the cylinders). The mechanism may also be utilized with a variety of mechanical assemblies, e.g., one or more cylinder assemblies, pressure vessels, motors (e.g., rotary motors), and/or turbines. The mechanism may remove fluid from an outlet of the mechanical assembly at elevated pressure and reintroduce the fluid at slightly higher pressure at an inlet of the mechanical assembly. This removal and reintroduction of fluid may result in expedited heat transfer to working gas in the mechanical assembly. Moreover, all of the mechanisms described above for converting potential energy in compressed gas to electrical energy, including the heat-exchange mechanisms and power electronics described, may, if appropriately designed, be operated in reverse to store electrical energy as potential energy in compressed gas. Since the accuracy of this statement will be apparent to any person reasonably familiar with the principles of electrical machines, power electronics, pneumatics, and the principles of thermodynamics, the operation of these mechanisms to store energy rather than to recover energy from storage will not be described. Such operation is, however, contemplated and within the scope of the invention and may be straightforwardly realized without undue experimentation.

In one aspect, embodiments of the invention feature an energy storage and recovery system suitable for the efficient use and conservation of energy resources. The system includes or consists essentially of a mechanical assembly for expansion and/or compression of a gas, and, in fluid communication with the mechanical assembly, a circulation apparatus. The mechanical assembly is configured to receive a heat-transfer fluid for maintaining the gas at a substantially constant temperature during the expansion and/or compression. To increase efficiency of the expansion and/or compression, the circulation apparatus receives pressurized heat-transfer fluid from an outlet of the mechanical assembly at a first elevated pressure, boosts a pressure of the heat-transfer fluid to a second pressure larger than the first pressure, and returns heat-transfer fluid to an inlet of the mechanical assembly at a third pressure.

Embodiments of the invention may include one or more of the following in any of a variety of combinations. The third pressure may range from approximately the first pressure to approximately the second pressure. The circulation apparatus may include or consist essentially of a pumping cylinder and an actuator. The pumping cylinder may include or consist essentially of two separated chambers and a piston disposed within the pumping cylinder separating the chambers. The actuator may be coupled to the piston and may alternately drive the piston in two opposing directions, thereby alternately increasing the pressure within each of the two chambers. A manifold assembly (i.e., including or consisting essentially of one or more manifolds) may be (i) selectively fluidly connected to both chambers of the pumping cylinder, and (ii) selectively fluidly connected to the inlet and the outlet of the mechanical assembly, such that each chamber alternatively receives the heat-transfer fluid from the mechanical assembly at the first pressure and returns the heat-transfer fluid to the inlet of the mechanical assembly at the second pressure. The actuator may include or consist essentially of (i) a linear actuator or (ii) a servo motor and ball-screw actuator.

The system may include a heat exchanger for thermally conditioning the heat-transfer fluid during circulation of the heat-transfer fluid. A mechanism (e.g., a spray mechanism such as a spray head and/or a spray rod) may introduce the heat-transfer fluid into the mechanical assembly.

The mechanical assembly may include or consist essentially of a cylinder assembly having (i) two separated compartments and (ii) a movable boundary disposed within the cylinder assembly separating the compartments. One or both of the compartments may be pneumatic. One of the compartments may be hydraulic. The movable boundary may include or consist essentially of a piston and rod assembly, which may define a fluid passageway therethrough connected to the outlet of the cylinder assembly.

A vessel for storage of compressed gas may be selectively fluidly connected to the mechanical assembly. A second circulation apparatus may be in fluid communication with the vessel. The second circulation apparatus may receive pressurized heat-transfer fluid from an outlet of the vessel at a fourth elevated pressure, boost a pressure of the heat-transfer fluid to a fifth pressure larger than the third pressure, and return the heat-transfer fluid to an inlet of the vessel at a sixth pressure. The sixth pressure may range between approximately the fourth pressure and approximately the fifth pressure.

In another aspect, embodiments of the invention feature a pumping system that includes or consists essentially of a pumping cylinder, an actuator, and a manifold assembly. The pumping cylinder includes or consists essentially of two separated chambers and a piston disposed within the pumping cylinder separating the chambers. The actuator is coupled to the piston and alternately drives the piston in two opposing directions, thereby alternately increasing a pressure within each of the two chambers. The manifold assembly is fluidly connected to both chambers of the pumping cylinder and selectively fluidly connectable to first and second fluid reservoirs such that each chamber alternately receives fluid from the first reservoir at a first pressure and returns fluid to the second reservoir at a second pressure higher than the first pressure.

Embodiments of the invention may include one or more of the following in any of a variety of combinations. The actuator may include or consist essentially of (i) a linear actuator or (ii) a servo motor and ball-screw actuator. The manifold assembly may include or consist essentially of two manifolds each comprising, mounted in parallel, two check valves mounted in opposing directions. Each check valve may include or consist essentially of a spring-return check valve. The pumping cylinder and the actuator may be mounted on a platform.

In yet another aspect, embodiments of the invention feature an energy storage system suitable for the efficient use and conservation of energy resources. The system includes or consists essentially of a vessel for storage of compressed gas and a circulation apparatus in fluid communication with the vessel. The vessel is configured to receive a heat-transfer fluid for thermally conditioning the gas. The circulation apparatus receives pressurized heat-transfer fluid from an outlet of the vessel at a first elevated pressure, boosts a pressure of the heat-transfer fluid to a second pressure larger than the first pressure, and returns heat-transfer fluid to an inlet of the vessel at a third pressure.

Embodiments of the invention may include one or more of the following in any of a variety of combinations. The third pressure may range between approximately the first pressure and approximately the second pressure. The circulation apparatus may include or consist essentially of a pumping cylinder and an actuator. The pumping cylinder may include or consist essentially of two separated chambers and a piston disposed within the pumping cylinder separating the chambers. The actuator may be coupled to the piston and may alternately drive the piston in two opposing directions, thereby alternately increasing the pressure within each of the two chambers. A manifold assembly (i.e., including or consisting essentially of one or more manifolds) may be (i) selectively fluidly connected to both chambers of the pumping cylinder, and (ii) selectively fluidly connected to the inlet and the outlet of the vessel, such that each chamber alternatively receives heat-transfer fluid from the vessel at the first pressure and returns heat-transfer fluid to the inlet of the vessel at the second pressure. The actuator may include or consist essentially of (i) a linear actuator or (ii) a servo motor and ball-screw actuator.

The system may include a heat exchanger for thermally conditioning the heat-transfer fluid during circulation of the heat-transfer fluid. A mechanism (e.g., a spray mechanism such as a spray head and/or a spray rod) may introduce the heat-transfer fluid into the vessel.

In a further aspect, embodiments of the invention feature an energy storage system suitable for the efficient use and conservation of energy resources. The system includes or consists essentially of a vessel for storage of compressed gas, a heat exchanger for thermally conditioning the gas, and a circulation apparatus. The heat exchanger is typically external to the vessel. The circulation apparatus receives pressurized gas from an outlet of the vessel at a first elevated pressure, boosts a pressure of the gas to a second pressure larger than the first pressure, circulates the gas through the heat exchanger to thermally condition the gas, and returns gas to an inlet of the vessel at a third pressure.

Embodiments of the invention may include one or more of the following in any of a variety of combinations. The third pressure may range between approximately the first pressure and approximately the second pressure. The circulation apparatus may include or consist essentially of a pumping cylinder and an actuator. The pumping cylinder may include or consist essentially of two separated chambers and a piston disposed within the pumping cylinder separating the chambers. The actuator may be coupled to the piston and may alternately drive the piston in two opposing directions, thereby alternately increasing the pressure within each of the two chambers. A manifold assembly (i.e., including or consisting essentially of one or more manifolds) may be (i) selectively fluidly connected to both chambers of the pumping cylinder, and (ii) selectively fluidly connected to the inlet and the outlet of the vessel, such that each chamber alternatively receives gas from the vessel at the first pressure and returns gas to the inlet of the vessel at the second pressure. The actuator may include or consist essentially of (i) a linear actuator or (ii) a servo motor and ball-screw actuator.

In yet a further aspect, embodiments of the invention feature a method of energy storage and recovery suitable for the efficient use and conservation of energy resources. Gas is stored, expanded, and/or compressed at an elevated pressure, and a heat-transfer fluid is circulated through the gas at the elevated pressure. The heat-transfer fluid is compressed to a second pressure higher than the elevated pressure, and, thereafter, heat-transfer fluid is introduced into the gas at a pressure ranging from approximately the elevated pressure to approximately the second pressure to thermally condition the gas. Embodiments of the invention may include one or more of the following in any of a variety of combinations. The gas may be stored, expanded, and/or compressed within a cylinder assembly. The heat-transfer fluid may be thermally conditioned outside of the cylinder assembly and/or after it is compressed. Between being compressed and being introduced into the gas, the pressure of the heat-transfer fluid may drop from approximately the second pressure to approximately the elevated pressure. Thermally conditioning the gas may include or consist essentially of heating the gas during expansion thereof and/or cooling the gas during compression thereof. Thermally conditioning the gas may include or consist essentially of pre-cooling the gas during storage thereof, and the gas may also be compressed. Thermally conditioning the gas may include or consist essentially of pre-heating the gas during storage thereof, and the gas may also be expanded. The heat-transfer fluid may be compressed in a pumping system that includes or consists essentially of a pumping cylinder and an actuator. The pumping cylinder may include or consist essentially of two separated chambers and a piston disposed within the pumping cylinder separating the chambers. The actuator may be coupled to the piston and may alternately drive the piston in two opposing directions, thereby alternately increasing a pressure within each of the two chambers.

These and other objects, along with advantages and features of the invention, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. Herein, the terms “liquid” and “water” interchangeably connote any mostly or substantially incompressible liquid, the terms “gas” and “air” are used interchangeably, and the term “fluid” may refer to a liquid or a gas unless otherwise indicated. As used herein, the terms “approximately” and “substantially” mean±10%, and, in some embodiments, ±5%. Note that as used herein the terms “pipe,” “piping” and the like refer to one or more conduits capable of carrying gas or liquid between two points. Thus, the singular term should be understood to extend to a plurality of parallel conduits where appropriate. As utilized herein, “elevated pressure” refers to a pressure above 0 psig, and “high pressure” refers to a pressure above approximately 250 psig, e.g., above approximately 1,000 psig, approximately 3,000 psig, or even higher. “Pressurized” fluids and gases are typically at elevated pressures, and may even be at high pressures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:

FIG. 1A is a schematic diagram of a system for the efficient pumping of a high-pressure fluid in accordance with various embodiments of the invention;

FIG. 1B is a schematic of a manifold and valve assembly arrangement for use in the system of FIG. 1A;

FIG. 2A shows the system of FIG. 1A in a different phase of operation;

FIG. 2B shows an exemplary embodiment of the system of FIG. 1A;

FIG. 3 is a schematic diagram of heat-transfer fluid being circulated efficiently through a vessel storing gas at high pressure, in accordance with various embodiments of the invention;

FIG. 4 is a schematic diagram of heat-transfer fluid being circulated efficiently through a pneumatic cylinder, in accordance with various embodiments of the invention; and

FIG. 5 is a schematic diagram in which pressure in a pipeline carrying fluid at high pressure is boosted, in accordance with various embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1A is a schematic diagram of a high-pressure pumping system 100 in accordance with various embodiments of the invention. The system 100 includes or consists essentially of a cylinder housing 101 containing a piston 102, a linear actuator 104 (shown as including or consisting essentially of a servo motor 104 a and ball-screw actuator 104 b), rods 110, 112; and valve manifolds 118, 120. System 100 may be connected to a pair of fluid bodies 106, 108 via pipes 122, 123, 124, 126, 128, and 129.

The piston 102 divides the cylinder housing 101 into a first chamber 114 and a second chamber 116, and slidably translates along the inner surfaces of the cylinder housing 101. In the embodiment shown, each of the rods 110, 112 is coupled to an opposite side of the piston 102 such that their axes align and each rod 110, 112 extends through seals (not shown) and beyond the boundaries (e.g., end caps) of the cylinder housing 101 (i.e., a double-rodded configuration). In alternative embodiments, two single-acting, single-rodded cylinders with a common rod are used in a similar fashion. As the piston 102 moves along the length of the cylinder housing 101, rod 112 feeds out of the cylinder housing 101, while the other rod 110 feeds in. Rods 110 and 112 are not necessarily two separate rods, but may be a single rod attached, e.g., near its midpoint, to the piston. This arrangement of cylinder housing 101, piston 102, and rods 110, 112 is capable of motion in both directions.

The linear actuator 104 imparts linear motion to the piston 102 through the rod 110. For example, a rotary electric servo motor 104 a may be attached to a ball-screw actuator 104 b to convert rotary motion to linear motion. Herein, “ball-screw actuator” denotes a screw embedded in a fixed sheath; between the external thread of the screw and the complementary internal thread of the sheath are ball bearings that reduce friction and transmit load as the screw turns. Alternatively, a linear electric motor may be used to apply force to the rod. Herein, “linear motor” denotes a device that exploits Faraday's Law to convert electromagnetic force in a circuit to a mechanical force acting along the axis of the device. Other devices (e.g., acme screw, power screw, rack and pinion), mechanical or electrical, may also be used to apply force to the rod 110. Any device used for this purpose is generally able to apply force in both directions. Herein, a device that applies force to the rod 110, whatever its nature, is referred to as an “actuator.” Herein, the rod 110 that is attached to the actuator 104 is referred to as the “working rod.”

Fluid bodies 106, 108 are sources of high-pressure fluids. In one embodiment, the first fluid body 106 is a source of heat-transfer fluid resident in a pneumatic cylinder and the second fluid body 108 is a heat-transfer fluid outputted by the cylinder housing 101 for delivery to the pneumatic cylinder. Generally, the first fluid body 106 is at a lower pressure (P₁, e.g., approximately 3,000 psig) than the higher-pressure second fluid body 108 (P₂, e.g., approximately 3,010 psig). The first fluid body 106 may represent the inlet state and the second fluid body 108 may represent the outlet state of the pumping system 100. The fluid bodies 106, 108 communicate with the first and second chambers 114, 116 of the cylinder housing 101 via an arrangement of external lines or pipes 122, 123, 124, 126, 128, and 129 in the configuration shown in FIG. 1A.

First and second manifold and valve assemblies (valve manifolds) 118, 120 control the flow of fluid into and out of the chambers 114, 116. (As used herein, the term manifold assembly refers to an assembly including one or more manifolds, e.g., valve manifolds 118, 120.) Each valve manifold 118, 120 includes a valve operating as an inlet and a valve operating as an outlet, as depicted for the first valve manifold 118 in FIG. 1B, with check valves 141, 142 (each of which may include or consist essentially of a spring-return check valve, as shown). The two check valves 141, 142 are typically oriented in opposing directions and attached in parallel via a common pipe 150 to a port disposed in the cylinder housing 101 (the first chamber 114 for the valve manifold 118, the second chamber 116 for the valve manifold 120). Check valve 141 is in communication with the lower-pressure (P₁) source 151 (fluid body 106 in FIG. 1A) via the pipes 122, 123 (or the pipes 122, 124 for the second valve manifold 120) such that fluid is admitted when pressure in the pipeline 150 drops below the lower pressure P₁ due to movement of the piston 102, acting as a refill valve for the pump chamber to which the pipeline 150 is attached. Check valve 142 is attached to the higher-pressure (P₂) body 152 (fluid body 108 in FIG. 1A) via the pipes 126, 129 (or the pipes 128, 129 for the second valve manifold 120) such that the fluid is allowed to flow out (i.e., to the body 152) when pressure in the pipe 150 rises above the higher pressure P₂. Besides check valves opened or closed by pressurized flow, the valve manifolds 118, 120 may include or consist essentially of electrically, pneumatically, manually, and/or hydraulically actuated valves.

In the operating state shown in FIG. 1A, the actuator 104 is acting on the rod 110 and causing it, the piston 102, and the rod 112 to move in the direction indicated by the arrow 130. Fluid in the second chamber 116 is compressed and raised to a pressure P₂′, slightly higher than the pressure P₂ of the fluid body 108. The fluid in the second chamber 116 flows through the second valve manifold 120 into the pipes 128, 129 to the fluid body 108. The fluid does not flow through the pipe 126 in this operating state, as check valve 142 prevents the flow of fluid.

Simultaneous with the raising of the pressure of the fluid in chamber 116 in the operating state shown in FIG. 1A, the pressure of the first chamber 114 is lowered by the action of the piston to P₁′, slightly lower than the pressure P₁ of the fluid body 106, causing the fluid to flow from the fluid body 106 through pipes 122 and 123 and through the valve manifold 118 into the first chamber 114 at a rate substantially equal to the rate at which the fluid is exiting the second chamber 116. (If the fluid being pumped is a liquid, the force exerted on rod 110 preferably does not cause cavitation anywhere in the system.) Fluid does not flow through pipe 124 in this operating state.

Reference is now made to FIG. 2A, which shows the illustrative embodiment of FIG. 1A in a second operating state. The actuator 104 reverses and begins to pull the rod 110, the attached piston 102, and the other rod 112 in the opposite direction (i.e., toward the actuator 104, as shown by arrow 230). At the beginning of this reverse stroke, the valves associated with each end of the cylinder housing 101 are set to new states, whether by external controls or by an intrinsic mechanism. Fluid in the first chamber 114 is raised to a pressure P₂′, slightly higher than the pressure P₂ of the fluid 108, and flows through the valve manifold 118 and the pipes 126, 129 to the fluid body 108. Fluid does not flow through pipe 128 in this operating state.

Simultaneously, the pressure of the second chamber 116 is lowered by the action of the piston to P₁′, slightly lower than the pressure P₁ of the fluid body 106, causing fluid to flow from the fluid body 106 through the pipes 122, 124 and through the valve manifold 120 into the second chamber 116 at a rate substantially equal to the rate at which fluid is exiting the first chamber 114. Fluid does not flow through pipe 123 in this operating state.

The difference between the inlet pressure P₁ and the outlet pressure P₂ is directly proportional to the magnitude of the force exerted by the actuator 104 on the working rod 110. Although no force is applied to the non-working rod 112 (i.e., the rod distal to the actuator 104) in the illustrated embodiment, it serves to make the area of the piston 102 acting on the fluid being pressurized substantially the same regardless of stroke direction. The pump 100 thus develops substantially identical pressure at its outlet regardless of stroke direction. A single-rodded cylinder may also be used in the identical setup with varying forces and/or pressures during different stroke directions.

Volumetric efficiency of the pump approaches 100%, and its mechanical efficiency may be determined by seal frictions, turbulence, and actuator efficiency. All components needed for the construction of the pump 100 in practice—for example, servo motor, ball screw actuator, cylinder-and-piston—are commonly known in the art. The accuracy of this statement will be apparent to any person familiar with the arts of mechanical engineering, electrical machines, and hydraulics. Embodiments of the invention have been described herein in terms of “high” input and output pressure but are, strictly speaking, independent of input pressure, from 0 psig up to the tolerance of the weakest component.

Reference is now made to FIG. 2B, which depicts an exemplary embodiment of a pump 200 in accordance with various embodiments of the invention. As shown, an electric servo motor 240 drives a ball-screw linear actuator 242, which pushes on one rod 244 (in a protective sheath) of a two-chamber, two-rodded cylinder 246 whose other rod 248 (also in a protective sheath) protrudes from the end of the pump 200. All components may be mounted on a platform 250 (e.g., a substantially rigid substrate such as a steel beam) to prevent deformation of the arrangement from the forces generated during operation. Other mounting arrangements, such as face-mounting of servo motor 240 to the actuator 242, may also be employed.

FIG. 3 depicts an illustrative application of an embodiment of the invention in an energy-storage system 300. In this application, the system 300 includes or consists essentially of a vessel 301 for the storage of compressed gas (which may correspond to a cylinder or cylinder assembly without a movable boundary mechanism therewithin and thus including only a single compartment), as well as a heat-transfer subsystem 305. The heat-transfer subsystem 305 includes or consists essentially of a heat exchanger 306 and a booster pump assembly 310 (which preferably corresponds to the pump 100 as described above). Vessel 301 may also or alternatively include other types of “containers” for compressed gas, including pipelines, bladders, caverns and other underground features, and various types (e.g., bags, bladders, domes) of underwater storage.

Operation of the system 300 may begin with the vessel 301 filled partly with a gas 302 at a high pressure P_(s) (e.g., approximately 3,000 psig) and partly with a heat-transfer fluid 304, also at pressure P_(s). The heat-transfer fluid 304 drains through an outlet of the vessel 301 and flows through a pipe 308 communicating with the pump 310, symbolized by a generic pump symbol. The pump 310 compresses and outputs the heat-transfer fluid 304 at a pressure P_(i)′ somewhat higher than P_(s) (e.g., approximately 3,015 psig). The compressed heat-transfer fluid 304 is sent through a pipe 312 to the heat exchanger 306, where its temperature is raised or lowered, and then through a pipe 316 to a spray mechanism 318 disposed inside the vessel 301. The compressed heat-transfer fluid 304 is typically introduced into the vessel 301 via the spray mechanism 318 at a different temperature than the gas 302 and, therefore, transfers thermal energy to or from the heat transfer fluid 304. Due to pressure drops in the pipes 312, 316, the heat exchanger 306, and the openings in the spray mechanism 318, the heat-transfer fluid 304 exits the spray mechanism 318 at a pressure P_(i) (e.g., approximately 3,000 psig) that is lower than the pump output pressure P_(i)′ (e.g., approximately 3,015 psig) and essentially equal to the pressure P_(s) (e.g., approximately 3,000 psig) within the vessel 301. Such a circulating system has a higher efficiency than a system that pumps liquid from a low intake pressure (e.g., 0 psig) to P_(i)′. Although spray mechanism 318 is depicted as a spray head disposed at one end of vessel 301, it may be supplemented or replaced by a perforated spray rod disposed within vessel 301 (e.g., substantially along the entire long axis of vessel 301).

In another embodiment, pump 310 circulates and boosts the pressure of gas 302 directly, and gas 302 is itself thermally conditioned by heat exchanger 306, in combination with or rather than thermal conditioning via introduction of heat-transfer fluid 304. In such embodiments, heat-transfer fluid 304 and/or spray mechanism 318 may be absent from vessel 301. Pump 310 may receive the pressurized gas 302 from the outlet of the vessel 301 at elevated pressure, boost the pressure of the gas 302, circulate the gas 302 through the heat exchanger 306 to thermally condition the gas 302, and return the gas 302 to the inlet of the vessel 301. Thus, the system has a higher efficiency due to the circulation and thermal conditioning of the gas 302 at elevated or high pressures.

The thermal conditioning of the gas 302 within vessel 301 may occur either as pre-heating prior to expansion or pre-cooling prior to compression in an energy storage and recovery system described herein (e.g., system 400 detailed below). As such, vessel 301 may be selectively fluidly connected (via, e.g., one or more valves not shown) to one or more cylinder assemblies (e.g., pneumatic and/or pneumatic/hydraulic cylinders) such that the pre-heated or pre-cooled gas is introduced therein for expansion or compression.

Reference is now made to FIG. 4, which depicts another illustrative application of the invention in an energy storage and recovery system 400. The system 400 includes or consists essentially of a pneumatic cylinder assembly 401 and a heat transfer subsystem 405. The heat transfer subsystem 405 includes or consists essentially of a heat exchanger 403 and a booster pump assembly 414 (which preferably corresponds to the pump 100 described above).

The pneumatic cylinder assembly 401 contains a piston 402 slidably disposed therein with a center-drilled rod 404 defining a fluid passageway extending from the piston 402. The rod 404 is also attached to, e.g., a mechanical load that is not depicted. In an initial state, the pneumatic cylinder assembly 401 may contain a gas 406 (introduced to the pneumatic cylinder assembly 401 via valves and pipes that are not shown) and a heat-transfer fluid 408 at a high pressure P_(s) (e.g., approximately 3,000 psig). As the gas 406 expands, it performs work on the piston 402. The heat-transfer fluid 408 flows through the center-drilled rod 404 and through a pipe 412 to the pump 414 (any fluid 409 on the other side of the piston 402 may flow through other valves and pipes that are not shown). The heat-transfer fluid 408 is also drawn to the pump 414 when lower pressure is generated during its operation. The pump 414 compresses and raises the pressure of the heat transfer fluid 408 to a pressure P_(i)′ somewhat higher than P_(s). (e.g., approximately 3,015 psig). The compressed heat-transfer fluid 408 is then sent through a pipe 416 to the heat exchanger 403, where its temperature is altered, and then through a pipe 418 to a spray mechanism 410 disposed within the pneumatic cylinder assembly 401. In one embodiment, the spray 411 of the heat-transfer fluid 408 is introduced into the pneumatic cylinder assembly 401 at a higher temperature than the gas 406 and, therefore, transfers thermal energy to the gas 406 and increases the amount of work done on the piston 402. In an alternative embodiment, the heat transfer fluid 408 is introduced at lower temperature than the gas 406 when the pneumatic cylinder assembly 401 is operated as a compressor. Due to pressure drops in the pipes 416, 418, the heat exchanger 403, and the openings of the spray mechanism 410, the heat-transfer fluid 408 generally exits the spray mechanism 410 at a pressure P_(i) (e.g., approximately 3,000 psig) that is lower than the pump output pressure P_(i)′ (e.g., approximately 3,015 psig) and essentially equal to the pressure P_(s) (e.g., approximately 3,000 psig) within the pneumatic cylinder assembly 401. Such a circulating system typically has higher efficiency than a system which pumps liquid from a low intake pressure (e.g., approximately 0 psig) to P_(i)′. Embodiments of the present invention may be utilized to inject heat-transfer liquid into one or more chambers of a pneumatic cylinder assembly, as described in U.S. patent application Ser. No. 12/690,513 (the '513 application), the entire disclosure of which is incorporated by reference herein. Although spray mechanism 410 is depicted as a spray head disposed at one end of pneumatic cylinder assembly 401, it may be supplemented or replaced by a perforated spray rod disposed within pneumatic cylinder assembly 401 (e.g., substantially along the entire long axis of pneumatic cylinder assembly 401).

Reference is now made to FIG. 5, which depicts another illustrative application of various embodiments of the present invention. A pipeline 500 contains fluid at a pressure P_(s). Due to frictional losses and work performed in creating fluid motion, this pressure P_(s) is lower than the injection pressure P_(i) at the inlet of the pipeline 500. In order to continue pumping the fluid and maintaining pressure in the pipe, a pump 502 (preferably corresponding to the pump 100 in FIG. 1) may be installed as a booster pump, as shown in FIG. 5. The pump 502 efficiently takes inlet fluid from the pipeline 500 at pressure P_(s), and outputs fluid at pressure P_(i) for injection into a downstream length of a pipeline 504.

Generally, the systems described herein may be operated in both an expansion mode and in the reverse compression mode as part of a full-cycle energy storage system with high efficiency. For example, the systems may be operated as both compressor and expander, storing electricity in the form of the potential energy of compressed gas and producing electricity from the potential energy of compressed gas. Alternatively, the systems may be operated independently as compressors or expanders.

In addition, the systems described above, and/or other embodiments employing liquid-spray heat exchange or external gas heat exchange (as detailed above), may draw or deliver thermal energy via their heat-exchange mechanisms to external systems (not shown) for purposes of cogeneration, as described in the '513 application.

The terms and expressions employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. 

1. An energy storage and recovery system suitable for the efficient use and conservation of energy resources, the system comprising: a mechanical assembly for at least one of expansion or compression of a gas, the mechanical assembly being configured to receive a heat-transfer fluid for maintaining the gas at a substantially constant temperature during the at least one of expansion or compression; and in fluid communication with the mechanical assembly, a circulation apparatus for receiving pressurized heat-transfer fluid from an outlet of the mechanical assembly at a first elevated pressure, boosting a pressure of the heat-transfer fluid to a second pressure larger than the first pressure, and returning heat-transfer fluid to an inlet of the mechanical assembly at a third pressure, to thereby increase efficiency of the at least one of expansion or compression.
 2. The system of claim 1, wherein the third pressure ranges from approximately the first pressure to approximately the second pressure.
 3. The system of claim 1, wherein the circulation apparatus comprises: a pumping cylinder comprising (i) two separated chambers, and (ii) a piston disposed within the pumping cylinder separating the chambers; and an actuator, coupled to the piston, for alternately driving the piston in two opposing directions, thereby alternately increasing a pressure within each of the two chambers.
 4. The system of claim 3, further comprising a manifold assembly (i) selectively fluidly connected to both chambers of the pumping cylinder, and (ii) selectively fluidly connected to the inlet and the outlet of the mechanical assembly, such that each chamber alternatively receives the heat-transfer fluid from the mechanical assembly at the first pressure and returns the heat-transfer fluid to the inlet of the mechanical assembly at the second pressure.
 5. The system of claim 3, wherein the actuator comprises a linear actuator.
 6. The system of claim 3, wherein the actuator comprises a servo motor and ball-screw actuator.
 7. The system of claim 1, further comprising a heat exchanger for thermally conditioning the heat-transfer fluid during circulation thereof.
 8. The system of claim 1, further comprising a mechanism for introducing the heat-transfer fluid into the mechanical assembly.
 9. The system of claim 8, wherein the mechanism for introducing the heat-transfer fluid comprises a spray mechanism.
 10. The system of claim 9, wherein the spray mechanism comprises at least one of a spray head or a spray rod.
 11. The system of claim 1, wherein the mechanical assembly comprises a cylinder assembly having (i) two separated compartments and (ii) a movable boundary disposed within the cylinder assembly separating the compartments.
 12. The system of claim 11, wherein at least one of the compartments is pneumatic.
 13. The system of claim 12, wherein both of the compartments are pneumatic.
 14. The system of claim 12, wherein one of the compartments is hydraulic.
 15. The system of claim 11, wherein the movable boundary comprises a piston and rod assembly.
 16. The system of claim 15, wherein the piston and rod assembly defines a fluid passageway therethrough connected to the outlet of the cylinder assembly.
 17. The system of claim 1, further comprising, selectively fluidly connected to the mechanical assembly, a vessel for storage of compressed gas.
 18. The system of claim 17, further comprising, in fluid communication with the vessel, a second circulation apparatus for receiving pressurized heat-transfer fluid from an outlet of the vessel at a fourth elevated pressure, boosting a pressure of the heat-transfer fluid to a fifth pressure larger than the fourth pressure, and returning heat-transfer fluid to an inlet of the vessel at a sixth pressure.
 19. The system of claim 18, wherein the sixth pressure ranges from approximately the fourth pressure to approximately the fifth pressure. 